Semiconductor lasers include edge-emitting lasers that emit a laser light at an edge of a semiconductor substrate, and surface-emitting lasers that emit a laser light from a surface of a semiconductor substrate. Surface-emitting lasers are characterized in that the laser emission angle is isotropic and small compared to edge-emitting lasers. When a surface-emitting laser is used as a light source for optical communications, for example, a large optical output is required. In order to increase the output of a surface-emitting laser, an enlargement of its laser emission aperture is effective. However, when the laser emission aperture is enlarged, the laser emission angle becomes larger. When the laser emission angle becomes larger, and for example, when the surface-emitting laser and an optical fiber are directly, optically coupled without a lens or the like, the optical coupling efficiency is lowered, and their mounting margin is reduced.
According to a conventional method to compose a smaller laser emission angle of a surface-emitting laser, an upper surface of a columnar section of a resonator of the surface-emitting laser is formed into a convex lens shape (lens layer or contact layer). An emitted light of the surface-emitting laser is converged by the lens layer or the contact layer, whereby the laser emission angle becomes smaller (for example, see FIG. 1, FIG. 7, and FIG. 8 of Japanese Laid-open Patent Application 2000-76682).
It is noted that, in the surface-emitting laser described with reference to FIG. 1, FIG. 7 and FIG. 8 of the aforementioned Japanese Laid-open Patent Application 2000-76682, the lens layer or the contact layer, which are formed in a lens shape, has an outer diameter that coincides with an outer diameter of the columnar section of the resonator. In actual surface-emitting lasers, the columnar section of the resonator is often provided with an outer diameter of 20 μm or greater. If the outer diameter of the columnar section is set to 20 μm or greater, and a sufficient lens curvature is to be provided to reduce the laser emission angle, the lens layer or the contact layer formed in a lens shape becomes too thick, and their manufacture becomes difficult.
On the other hand, a surface-emitting laser described with reference to FIG. 10 of the aforementioned Japanese Laid-open Patent Application 2000-76682 includes an entire columnar section of the resonator that is formed into a lens shape. In this manner, the curvature of the lens shape can be made smaller, and the laser emission angle can be made smaller. However, in such a conventional surface-emitting laser, because the entire columnar section of the resonator is formed into a curved surface, a sufficient contact surface cannot be provided between an upper electrode (an anode electrode or a cathode electrode of the surface-emitting laser) and the contact layer. Accordingly, the conventional surface-emitting laser has a problem in that an element resistance (resistance between an anode electrode and a cathode electrode) becomes higher.